1. Field of the Invention
The present invention relates to a process for preparing conductive or semiconducting structured polymers.
In microelectronics, photoresists are widely used for a variety of lithographic technologies. Normally, a photoresist layer is applied to a substrate that is to be structured (or patterned) and subsequently exposed. Following the exposure, the photoresist layer is developed so that, depending on whether it is a positive or a negative resist, the exposed portions of the photoresist layer are removed by the developer or the unexposed portions of the photoresist are removed by the developer.
Thereafter, the structured photoresist layer is used as an etch mask for the etching of the substrate. In this procedure, the structure of the structured photoresist layer is transferred into the substrate. Normally, the photoresist layer is then removed from the substrate. Accordingly, the photoresist layer is an auxiliary layer which is used for structuring the substrate and then removed again. Customary photoresist layers are nonconducting, thereby preventing short circuits due to incompletely removed photoresist residues.
The prior art has disclosed, for example, what are known as chemically amplified resists (CARs) for lithographic technologies and processes. The CAR photoresists can be used in accordance with the principle of acid-catalytic cleavage. In accordance with this principle, in the case of positive-working photoresists, a polar carboxylic acid group is formed from an apolar chemical group, such as a tert-butyl carboxylate group, for example, in the presence of a photolytically generated acid. In a subsequent developing step, the exposed photoresist layer is treated with aqueous-alkaline developer solutions, with the polar regions rich in carboxylic acid being dissolved and the unexposed regions of the resist remaining. Reference is had, in this context, to the description in Solid State Technology, Vol. 39 (1996), No.7, pages 164–173.
In a process known from European patent document EP 0 395 917 for the subsequent processing of photoresist structures which have already been developed, a special kind of photoresist system developable by aqueous alkali is used. In this case, a base polymer is used in the resist that contains further reactive groups. The groups allow the developed resist structure to be aftertreated with appropriate reagents. In the course of the aftertreatment, the structures are widened (chemical amplification of resist lines: CARL) and the resist trenches and resist holes narrowed, leading among other things to an enlargement of the processing window during production.
In accordance with a process known from U.S. Pat. No. 5,234,793, the aftertreatment is utilized for silylation in a two-layer resist system (SI-CARL).
Chemically amplified photoresists are also known from Advanced Materials for Optics and Electronics, Vol. 4 (1994), pages 83–93.
The purpose of the abovementioned photoresists is to serve as etch masks for structuring a substrate, and then to be removed.
Organic semiconductors and electronic components based on polymer electronics offer an attractive alternative to conventional inorganic components. The reason for this attractiveness lies, for example, in low production costs, simple packing, and compatibility with flexible substrates. By way of example, organic p-semiconductors are already known from Römpp, Lexikon der Chemie, Thieme-Verlag. Examples of organic p-semiconductors are polypyrrole, poly(phenylene-vinylene) or doped polyacetylene.
In their original chemical form, semiconducting and conducting polymers are very difficult to process owing to their conjugated double bond structure. Because of the rigid polymer structure caused by the double bonds, these polymers are in particular often of sparing to zero solubility even in suitable process solvents. Increasing the solubility and hence enhancing the processability needed for producing a film having a certain minimum thickness requires complex chemical modifications of the conductive organic polymer molecules. By means of suitable chemical modification of the semiconducting or conducting organic starting substances it is possible to increase the solubility, at least to some extent. This is described, for example, in Physics World, March 1999, pages 31–34. In this case the solubility can be increased by attaching suitable flexible, long sidechains. To do so, however, requires considerable synthesis effort, since it is necessary to retain the conductivity of the molecules during chemical modification, thereby increasing the costs.